The molding of thermoset polymers is a technologically and commercially important processing technique. In one known version of this technique, a liquid cyclic olefin monomer resin is combined with a single metal carbene olefin metathesis catalyst to form a prior art ROMP composition, and the prior art ROMP composition is added (e.g., poured, cast, infused, injected, etc.) into a mold. The prior art ROMP composition is subjected to conditions effective to polymerize the prior art ROMP composition and on completion the molded article is removed from the mold for any optional post cure processing that may be required. For purposes of this disclosure it is important to emphasize that the term “prior art ROMP composition(s)” as used herein are those ROMP compositions which are formed by combining a liquid cyclic olefin monomer resin with only one metal carbene olefin metathesis catalyst (i.e., a single metal carbene olefin metathesis catalyst). As is known in the art, the liquid cyclic olefin monomer resin may optionally contain added modifiers, fillers, reinforcements, flame retardants, pigments, etc. Examples of such prior art ROMP compositions are disclosed in U.S. Pat. Nos. 5,342,909; 6,310,121; 6,515,084; 6,525,125; 6,759,537; 7,329,758, etc.
To successfully mold an article, it is important to be able to control the rate at which a ROMP composition polymerizes. As polymerization progresses, the viscosity of the ROMP composition increases, progressing from a liquid state, through a gel state, to the final hard polymer. At some point during this progression, the temperature generally begins to increase rapidly leading to a sharp exotherm. The viscosity of the ROMP composition must not increase too rapidly (build up too rapidly) before the ROMP composition can be introduced into the mold. In addition, the ROMP composition must not gel or exotherm (i.e., cure) before it can be introduced into the mold. Furthermore, the ROMP composition must not gel or exotherm before the mold is completely filled or before the catalyst has had sufficient time to completely disperse in the monomer. However, in some cases, for convenience and expedient cycle time, it may be important that the catalyst initiates polymerization of the monomer and the ROMP composition exotherms within a reasonable time after the mold is filled.
A general issue with molding articles with a prior art ROMP composition is that many of the metal carbene olefin metathesis catalysts (e.g., ruthenium metal carbene olefin metathesis catalysts) react rapidly with cyclic olefins and therefore are not particularly suitable for molding a wide array of polymer articles, such as large articles, composite articles, articles having complex geometries and/or areas of varying thickness, and/or articles which have thicknesses greater than ¼″.
A particular issue with molding articles using prior art ROMP compositions is that various regions or sections of the article being molded may possess different degrees or states of polymerization (e.g., liquid, soft gel, hard polymer gel, exotherm) during the molding cycle. For example, during the molding of an article a prior art ROMP composition may be in a gelled state in one section or region of a mold and in a liquid state in another section or region of the mold. This is particularly problematic if the prior art ROMP composition begins to exotherm in one section of the mold, but is still in a liquid state in another section of the mold. The greater the amount of liquid cyclic olefin monomer present in a ROMP composition when the ROMP composition begins to exotherm the more likely the molded article will either possess defects requiring repair or need to be discarded, which in either situation leads to increased manufacturing costs. Without being bound by theory, certain defects in the molded article are thought to be formed when liquid cyclic olefin monomer (e.g., dicyclopentadiene) present in a ROMP composition is volatized (converted from a liquid state to a gaseous state) as a result of the high temperatures generated during exotherm of the ROMP composition.
In addition, the issue of volatilization of liquid cyclic olefin monomer has been found to be problematic during the molding of an article using prior art ROMP compositions, particularly when using a heated mold, where one mold surface may be at a higher temperature than another mold surface or where there is a temperature differential between the mold surfaces. This issue is exacerbated when molding composite articles, particularly thick composite articles or highly filled composite articles, as the substrate material (e.g., reinforcement material) may function as a heat sink, effectively cooling the prior art ROMP composition as it permeates through and/or around the substrate material when filling the mold cavity. In this situation, the portion of the prior art ROMP composition farthest from the heated mold surface may still be in a liquid state when the portion of the prior art ROMP composition closest to the heated mold surface begins to exotherm, thereby resulting in defects in the molded article due to volatilization of liquid cyclic olefin monomer.
Generally, it would be useful and commercially important to be able to control the rate of reaction of catalyzed metathesis reactions, particularly ROMP reactions. It would be particularly useful and commercially important to be able to control the rate of polymerization of a cyclic olefin resin composition catalyzed with a metal carbene olefin metathesis catalyst (e.g., a ruthenium or osmium carbene olefin metathesis catalyst). Moreover, it would be particularly useful and commercially important during the molding of an article to be able to control the polymerization of a ROMP composition in such a way that the liquid cyclic olefin monomer present in the ROMP composition has reached a uniformly formed gelled state throughout the different regions/sections of a mold or throughout the ROMP composition before the ROMP composition begins to exotherm. More specifically, it would be particularly useful and commercially important to have a means to independently control the time required for the ROMP composition to reach a hard polymer gel relative to the exotherm time.
Previously, there have been few methods for controlling the rate of polymerization of a cyclic olefin resin composition catalyzed with a metal carbene olefin metathesis catalyst (e.g., a ruthenium or osmium carbene olefin metathesis catalyst). One method for controlling the rate of polymerization of a prior art ROMP composition is by controlling/adjusting the temperature of the resin composition and/or the mold. Unfortunately, as is demonstrated in Table 11 infra, adjustment of the temperature of the resin composition and/or mold does not enable independent control over the time required for a prior art ROMP composition to reach a hard polymer gel relative to the exotherm time. In other words, following the catalyzation of a cyclic olefin resin composition with a single metal carbene olefin metathesis catalyst to form a prior art ROMP composition, the time for the prior art ROMP composition to reach a hard polymer gel and the time for the prior art ROMP composition to exotherm both decrease when the composition temperature and/or mold temperature is increased. Conversely, following the catalyzation of a cyclic olefin resin composition with a single metal carbene olefin metathesis catalyst to form a prior art ROMP composition, the time for the prior art ROMP composition to reach a hard polymer gel and the time for the prior art ROMP composition to exotherm both increase when the composition temperature and/or mold temperature is decreased.
Another method for controlling the rate of polymerization of a cyclic olefin resin composition catalyzed with a single metal carbene olefin metathesis catalyst (e.g., a ruthenium or osmium carbene olefin metathesis catalyst) has been disclosed in U.S. Pat. No. 5,939,504 and International Pat. App. No. PCT/US2012/042850, the contents of both of which are incorporated herein by reference. Here, exogenous (meaning external additive or other reactives that can be added to the resin composition, or mixed or combined with the single carbene catalyst) is distinguished from indigenous (meaning native or established by the components attached to the transition metal of the single carbene catalyst). U.S. Pat. No. 5,939,504 discloses the use of exogenous “gel modification additives” or exogenous inhibitors, such as a neutral electron donor or a neutral Lewis base, preferably trialkylphosphines and triarylphosphines, to modify the pot life of a prior art ROMP composition. International Pat. App. No. PCT/US2012/042850 discloses the use of exogenous hydroperoxide gel modifiers or exogenous inhibitors, such as cumene hydroperoxide, to modify the pot life of a prior art ROMP composition. The time during which a ROMP composition can be worked after the resin composition and the metal carbene olefin metathesis catalyst are combined is called the pot life.
While the use of exogenous inhibitors continues to be a valuable method for controlling the pot life of a prior art ROMP composition, the use of exogenous inhibitors has numerous limitations and several improvements are both needed and desired. Unfortunately, as is demonstrated in Table 12 infra, the use of exogenous inhibitors (e.g., triphenylphosphine or cumene hydroperoxide) in a prior art ROMP composition does not enable independent control over the time required for the prior art ROMP composition to reach a hard polymer gel relative to the exotherm time. In other words, following the formation of a prior art ROMP composition, the time for the prior art ROMP composition to reach a hard polymer gel and the time for the prior art ROMP composition to exotherm both increase when the concentration of exogenous inhibitor is increased. Conversely, following the formation of a prior art ROMP composition, the time for the prior art ROMP composition to reach a hard polymer gel and the time for the prior art ROMP composition to exotherm both decrease when the concentration of exogenous inhibitor is decreased. However, use of higher amounts of exogenous inhibitor in a prior art ROMP composition may have undesirable effects on the properties of a polymer and/or polymer composite formed from the prior art ROMP composition (e.g., decreased mechanical and/or thermal properties).
Another previously known method for controlling the rate of a catalyzed metathesis reaction is through the modification of the character of the ligands attached to the ruthenium or osmium transition metal of the carbene olefin metathesis catalyst (indigenous modification). For example, RuCl2(PPh3)2(═CHPh) reacts more slowly with cyclic olefins than RuCl2(PCy3)2(═CHPh), while RuCl2(PPh3)sIMes(=CHPh) reacts more rapidly with cyclic olefins than RuCl2(PCy3)sIMes(=CHPh), where sIMes represents 1,3-Bis(2,4,6-trimethylphenyl)-2-imidazolidinylidene and Cy represents cyclohexyl. Furthermore, ligand modification, for example, has been used to prepare latent metal carbene olefin metathesis catalysts such as C771, C835, and C871 disclosed herein. Several other latent metal carbene olefin metathesis catalysts for ROMP are known and have been disclosed in U.S. Pat. Appl. Pub. Nos. 2005/0261451 and 2012/0271019, U.S. Pat. No. RE38676, etc. Unfortunately, as is demonstrated infra, latent metal carbene olefin metathesis catalysts (e.g., latent ruthenium or osmium olefin metathesis catalysts) do not enable independent control over the time required for a prior art ROMP composition to reach a hard polymer gel relative to the exotherm time.
Another previously known method for controlling the rate of polymerization of a cyclic olefin resin composition has been disclosed in U.S. Pat. No. 6,162,883 where a catalyst mixture of a thermal carbene-free ruthenium catalyst and a thermal ruthenium carbene catalyst were used to generate a latent catalyst for the ROMP of strained cycloolefins. However, U.S. Pat. No. 6,162,883 does not address the issues associated with the volatilization of liquid cyclic olefin monomer during ROMP of a liquid cyclic olefin monomer resin, nor does it provide solutions to address these issues. Moreover, U.S. Pat. No. 6,162,883 does not address the issue of enabling independent control over the time required for a ROMP composition to reach a hard polymer gel relative to the exotherm time.
Therefore, despite advances achieved in the art, particularly in properties of olefin metathesis polymers and their associated applications, a continuing need therefore exists for further improvement in a number of areas, including methods and compositions for catalyzing and controlling olefin metathesis reactions, particularly ROMP reactions.